Gasification system and method

ABSTRACT

A system configured for the production of at least one product selected from the group consisting of syngas, Fischer-Tropsch synthesis products, power, and chemicals, the system comprising a dual fluidized bed gasification apparatus and at least one apparatus selected from power production apparatus configured to produce power from the gasification product gas, partial oxidation reactors configured for oxidation of at least a portion of the product gas, tar removal apparatus configured to reduce the amount of tar in the product gas, Fischer-Tropsch synthesis apparatus configured to produce Fischer-Tropsch synthesis products from at least a portion of the product gas, chemical production apparatus configured for the production of at least one non-Fischer-Tropsch product from at least a portion of the product gas, and dual fluidized bed gasification units configured to alter the composition of the product gas. Methods of operating the system are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application No. 61/512,365, filed Jul. 27, 2011, thedisclosure of which is hereby incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

1. Field of the Invention

This disclosure relates generally to the field of gasification. Morespecifically, the disclosure relates to a system and method for theproduction of synthesis gas via gasification of carbonaceous materials.Still more specifically, the disclosed system and method are suitablefor the production of synthesis gas for use in the Fischer-Tropschsynthesis of hydrocarbons, the production of power, the production ofnon-Fischer-Tropsch chemicals/fuels, or a combination thereof.

2. Background of Invention

Gasification is utilized to produce process gas suitable for theproduction of various chemicals, for the production of Fischer-Tropschliquid hydrocarbons, and for the production of power. Many feedmaterials serve as carbonaceous sources for gasification, including, forexample, shredded bark, wood chips, sawdust, sludges (e.g., sewagesludge), municipal solid waste, RDF, and a variety of other carbonaceousmaterials.

Fischer-Tropsch (FT) synthesis represents a catalytic method for thecreation of synthetic liquid fuels. The reaction occurs by the metalcatalysis of an exothermic reaction between carbon monoxide and hydrogengas in mixtures known as synthesis gas, or ‘syngas’. The liquid productof the reaction is typically refined to produce a range of syntheticfuels, lubricants and waxes. The primary metals utilized as catalystsare cobalt and iron. Providing synthesis gas having a desired molarratio of hydrogen to carbon monoxide is necessary for economicproduction of Fischer-Tropsch synthesis products.

There is a need in the art for improved systems and methods ofgasification, whereby materials (that may be generally considered waste)may be converted to gas suitable for the production of power and/or forthe production of various chemicals and/or fuels (including, withoutlimitation, Fischer-Tropsch synthesis products).

SUMMARY

Herein disclosed is a system configured for the production of at leastone product selected from the group consisting of synthesis gas,Fischer-Tropsch synthesis products, power, and chemicals, the systemcomprising: a dual fluidized bed gasification apparatus including agasifier and a combustor, wherein the combustor is configured forheating a particulate heat transfer material, thus producing a combustorflue gas; and wherein the gasifier is configured to receive the heatedparticulate heat transfer material and a carbonaceous feedstock, wherebythe heated particulate heat transfer material provides heat forendothermic gasification of the carbonaceous feedstock, thus producing agasification product gas comprising hydrogen and carbon monoxide; and atleast one apparatus selected from the group consisting of powerproduction apparatus configured to produce power from at least a portionof the gasification product gas, partial oxidation reactors configuredfor oxidation of at least a portion of the gasification product gas, tarremoval apparatus configured to reduce the amount of tar in thegasification product gas, Fischer-Tropsch synthesis apparatus configuredto produce Fischer-Tropsch synthesis products from at least a portion ofthe gasification product gas, chemical production apparatus configuredfor the production of at least one non-Fischer-Tropsch product from atleast a portion of the gasification product gas, and dual fluidized bedgasification units configured to alter the composition of at least aportion of the gasification product gas.

In embodiments, the system comprises Fischer-Tropsch synthesisapparatus. The Fischer-Tropsch synthesis apparatus may be operable withan iron-based Fischer-Tropsch catalyst; and (a) the dual fluidized bedgasification apparatus is operable to provide a gasification product gashaving a molar ratio of hydrogen to carbon monoxide that is in the rangeof from about 0.5:1 to about 1.5:1, (b) the system further comprisesapparatus configured to adjust the molar ratio of hydrogen to carbonmonoxide in at least a portion of the gasification product gas to avalue in the range of from about 0.5:1 to about 1.5:1, or both (a) and(b). In embodiments, the Fischer-Tropsch synthesis apparatus is operablewith a cobalt-based Fischer-Tropsch catalyst; and (a) the dual fluidizedbed gasification apparatus is operable to provide a gasification productgas having a molar ratio of hydrogen to carbon monoxide in the range offrom about 1.5:1 to about 2.5:1, (b) the system further comprisesapparatus configured to adjust the molar ratio of hydrogen to carbonmonoxide in at least a portion of the gasification product gas to avalue in the range of from about 1.5:1 to about 2.5:1, or both (a) and(b). The Fischer-Tropsch synthesis apparatus may comprise at least oneFischer-Tropsch synthesis reactor configured to produce non-gaseousFischer-Tropsch synthesis products from at least a portion of thegasification product gas. The Fischer-Tropsch synthesis reactor may befurther operable to provide a Fischer-Tropsch tailgas. In suchembodiments, the system may further comprise a recycle line whereby atleast a portion of the Fischer-Tropsch tailgas can be introduced intothe dual fluidized bed gasification apparatus. In embodiments, at leasta portion of the Fischer-Tropsch tailgas is introduced into a systemcomponent selected from the group consisting of the combustor, thegasifier, and seal pots configured to prevent backflow of material fromthe combustor or from the gasifier.

The system may comprise power production apparatus. The power productionapparatus may comprise a gas turbine.

In embodiments, the system comprises a Fischer-Tropsch synthesisapparatus comprising a solid/liquid separator configured for separatinga spent catalyst product comprising Fischer-Tropsch catalyst andFischer-Tropsch synthesis product from the non-gaseous Fischer-Tropschsynthesis products. Such a system may further comprise one or morerecycle lines configured to introduce at least a portion of the spentcatalyst product into the dual fluidized bed gasification apparatus. Thesystem may comprise at least one recycle line selected from the groupconsisting of recycle lines fluidly connecting the solid/liquidseparator with the combustor, whereby spent catalyst product can beintroduced into the combustor for use as fuel; and recycle lines fluidlyconnecting the solid/liquid separator with the gasifier, wherebyadditional product gas can be produced via gasification of at least aportion of the spent catalyst product.

In embodiments, the gasifier is configured to convert at least a portionof the carbonaceous feedstock to char and the system is configured fortransfer of the char out of the gasifier. In embodiments, the system isconfigured for transfer of at least a portion of the char to thecombustor, and the combustor is configured to combust the char toprovide at least a portion of the heat for heating the particulate heattransfer material. In embodiments, the combustor is configured foroperation with substantially no fuel other than the char. Inembodiments, the combustor is configured for operation with asupplemental fuel selected from the group consisting of tar,Fischer-Tropsch wax, Fischer-Tropsch tailgas, upgrader tailgas, refinerytank bottoms, heavy fuel oil, liquid fuel oil, and combinations thereof.

In embodiments, the system comprises a tar removal apparatus, and thesupplemental fuel to the combustor comprises tar removed via the tarremoval apparatus. In embodiments, the system comprises a tar removalapparatus, and the system further comprises at least one recycle lineselected from the group consisting of recycle lines fluidly connectingthe tar removal apparatus with the combustor, whereby at least a portionof the tar removed via the tar removal apparatus can be combusted toheat the particulate heat transfer material; and recycle lines fluidlyconnecting the tar removal apparatus with the gasifier, whereby at leasta portion of the tar removed via the tar removal apparatus can begasified to provide additional gasification product gas.

In embodiments, the system comprises Fischer-Tropsch synthesisapparatus, and the supplemental fuel to the combustor comprisesFischer-Tropsch tailgas, Fischer-Tropsch wax (e.g. liquid FT products),or both produced in the Fischer-Tropsch synthesis apparatus.

In embodiments, the system comprises Fischer-Tropsch synthesis apparatusand upgrading apparatus located downstream of the Fischer-Tropschsynthesis apparatus, and the supplemental fuel to the combustorcomprises upgrader tailgas produced in the upgrading apparatus.

In embodiments, the gasifier is configured for operation at a gasifierpressure and the combustor is configured for operation at a combustorpressure in the range of from about 0 psig to a pressure that is atleast 2 psig less than the gasifier pressure.

In embodiments, the gasifier is configured to provide an entrainedproduct comprising particulate heat transfer material entrained ingasification product gas, and the system comprises at least oneparticulate separator selected from the group consisting of gasifierparticulate separators configured to separate gasification product gasfrom the entrained product; and combustor particulate separatorsconfigured to separate heated particulate heat transfer material fromthe combustor flue gas. Such a system may further comprise at least oneexpander downstream of at least one combustor particulate separator. Thesystem may further comprise heat recovery apparatus downstream of the atleast one expander. The system may comprise at least one combustorparticulate separator that is a cyclone, and the at least one combustorcyclone may be operable at a superficial velocity in the range of fromabout 70 to about 85 ft/s.

In embodiments, the system comprises (a) at least one primary gasifierparticulate separator configured to separate particulate heat transfermaterial from the entrained product, thus providing aparticulate-reduced product comprising ash, and at least one secondarygasifier particulate separator configured to separate particulate heattransfer material from the particulate-reduced product, (b) at least oneprimary combustor particulate separator configured to separateparticulate heat transfer material from the flue gas, thus providing aparticulate-reduced flue gas comprising ash, and at least one secondarycombustor particulate separator configured to separate particulate heattransfer material from the particulate-reduced flue gas; or both (a) and(b). Such a system may be configured for introduction of the separatedparticulate materials from the primary gasifier particulate separator,the secondary gasifier particulate separator, or both into the combustorfor heating therein and/or may further comprise a scrubber downstream ofthe secondary gasifier particulate separator, a scrubber downstream ofthe secondary combustor particulate separator, or both, wherein thescrubber is configured to scrub sulfur from a gas introduced thereto,via contact thereof with a liquid comprising at least a portion of theash. In embodiments, the at least one primary gasifier particulateseparator, the at least one primary combustor particulate separator, orboth is configured for removal of greater than 99, 99.9, or 99.98 weightpercent of the particulate heat transfer material from a gas introducedthereto. In embodiments, the at least one secondary gasifier particulateseparator, the at least one secondary combustor particulate separator,or both is configured for removal of greater than about 60, 70, 80, 85,or 90 weight percent of the ash from a gas introduced thereto.

Various embodiments of the system comprise one or more heat recoveryapparatus configured for recovery of heat from the gasification productgas, from the combustor flue gas, or from both the gasification productgas and the combustor flue gas. In embodiments, the system comprises tarremoval apparatus, and heat recovery apparatus configured forutilization of the heat from the gasification product gas, wherein theheat recovery apparatus is configured to reduce the temperature of thegasification product gas to no less than about 800° F., 700° F., or 600°F. upstream of the tar removal apparatus. The at least one heat recoveryapparatus may comprise at least one component selected from the groupconsisting of air preheaters, boiler feedwater preheaters, steamsuperheaters, waste heat boilers, waste heat superheaters, andeconomizers. In embodiments, the system comprises an air preheaterconfigured to recover heat from the gasification product gas andintroduce heated air into the combustor. In embodiments, the systemcomprises (a) at least one heat recovery apparatus located downstream ofthe at least one primary gasifier particulate separator, (b) at leastone heat recovery apparatus located downstream of the at least oneprimary combustor particulate separator, or both (a) and (b). Inembodiments, the system comprises (a) at least one heat recoveryapparatus located upstream of the at least one secondary gasifierparticulate separator, (b) at least one heat recovery apparatus locatedupstream of the at least one secondary combustor particulate separator,or both (a) and (b). In embodiments, the system comprises at least onesecondary particulate separator located downstream of the at least oneheat recovery apparatus and operable at a temperature of less than about400° F.

In embodiments, the system comprises heat recovery apparatus downstreamof at least one particulate separator. In embodiments, the systemcomprises at least one sealing apparatus selected from seal pots andvalves configured to prevent backflow of material from the combustorinto the at least one gasifier particulate separator or from thegasifier into the at least one combustor particulate separator. Thevalve may be selected from J-valves and L-valves. In embodiments, thesystem comprises a J-valve configured to prevent backflow of materialfrom the gasifier into the at least one combustor particulate separator.In embodiments, the system comprises at least one seal pot selected fromcombustor seal pots configured to prevent backflow of material from thecombustor into the at least one gasifier particulate separator andgasifier seal pots configured to prevent backflow of material from thegasifier into the at least one combustor particulate separator. The atleast one seal pot may be configured for operation at a minimumfluidization velocity of greater than about 0.2 ft/s. The at least oneseal pot may be configured for operation at a minimum fluidizationvelocity of greater than about 1.5 ft/s. The pressure drop across the atleast one seal pot may be at least 2 psig, and/or less than about 20psig. In embodiments, the at least one particulate separator comprises adipleg extending from at or near a bottom thereof, and the diplegextends a distance into the at least one seal pot from at or near a topthereof. The at least one seal pot may comprise a distributor and thedipleg of the at least one particulate separator may extend to adistance no less than about 10, 11, 12, 13, 14, 15, 16, 17, or 18 inchesfrom the seal pot distributor. In embodiments, the minimum distance fromthe dipleg to a side or bottom of the seal pot is at least 10 inches.

In embodiments, the system comprises at least two gasifier particulateseparators, each comprising a dipleg extending a distance into acombustor seal pot; at least two combustor particulate separators, eachcomprising a dipleg extending a distance into a gasifier seal pot; orboth, wherein the minimum dipleg to dipleg separation within a seal potis at least 10 inches. In embodiments, an angle selected from the groupconsisting of an angle formed between an at least one combustor seal potand the combustor and an angle formed between an at least one gasifierseal pot and the gasifier is in the range of from about 5° to about 90°.In embodiments, the angle is less than about 45°. In embodiments, thesystem comprises at least one combustor seal pot, and the at least onecombustor seal pot is fluidized by a combustor seal pot fluidizationgas. The combustor may be configured for fluidization with a combustorfluidization gas (which may be introduced via line 121) comprisingprimarily air or oxygen. In embodiments, the combustor is configured foroperation with excess oxygen in the range of from about 0 to about 20volume percent. In embodiments, at least or about 20% of the combustorfluidization gas needed in the combustor is introduced via at least onecombustor seal pot. The at least one seal pot may be substantially roundor substantially rectangular. In embodiments, the at least one seal potis substantially rectangular and the operating pressure of the at leastone rectangular seal pot is less than about 15 psig.

In embodiments of the system, the particulate heat transfer material isselected from the group consisting of sand, limestone, and othercalcites or oxides including iron oxide, olivine, and magnesia, alumina,carbides, silica alumina, zeolites, and combinations thereof. Theparticulate heat transfer material may comprise a catalyst.

In embodiments, the system comprises a carbonaceous material feed inletfluidly connected with the gasifier, and configured for introduction ofthe carbonaceous feedstock into the gasifier. In embodiments, an angleformed between the carbonaceous material feed inlet and the gasifier isin the range of from about 5° to about 20°. The carbonaceous feedstockmay comprise at least one material selected from the group consisting ofbiomass, RDF, MSW, sewage sludge, coal, Fischer-Tropsch synthesis wax,and combinations thereof. In embodiments, the gasifier is operable withcarbonaceous feedstocks at any temperature in the range of from about−40° F. to about 260° F. The system may be configured for introductionof a purge gas with the carbonaceous feedstock. The purge gas may beselected from the group consisting of carbon dioxide, steam, fuel gas,nitrogen, synthesis gas, combustor flue gas, and combinations thereof.The system may comprise apparatus (e.g. downstream apparatus 100) forthe removal of carbon dioxide from the combustor flue gas, thegasification product gas, or both; and one or more recycle lines fluidlyconnecting the carbon dioxide removal apparatus (e.g. via line 115) witha gasifier carbonaceous material feed inlet, whereby at least a portionof the removed carbon dioxide can be introduced into the gasifier aspurge gas.

In embodiments, the combustor is operable such that an operatingtemperature at or near an inlet thereto for heat transfer material is inthe range of from about 1000° F. to about 1400° F., and an operatingtemperature at or near the exit thereof to a combustor particulateseparator is in the range of from about 1400° F. to about 1800° F. Thesystem may comprise a dryer upstream of the gasifier, wherein the dryeris configured to remove moisture from the carbonaceous feedstock priorto introduction thereof into the gasifier. The system may comprise aline configured for introducing at least a portion of the combustor fluegas into the dryer, whereby hot combustor flue gas can be utilized todry the carbonaceous feedstock. In embodiments, the gasifier is operablewith a carbonaceous feedstock having a moisture content in the range offrom about 10 to about 40 weight percent.

The system may be operable to convert at least about 30, 40, 50, 60, 70,or 80% of the carbon in the carbonaceous feedstock into gasificationproduct gas. In embodiments, the gasifier is operable at a carbonaceousfeedstock rate of at least 2000 lb/h-ft², 2400 lb/h-ft², 2500 lb/h-ft²,3000 lb/h-ft², 3400 lb/h-ft², or 4000 lb/h-ft². In embodiments, thegasifier is configured for fluidization with a gasifier fluidization gashaving an inlet gasifier fluidization gas superficial velocity in therange of from about 0.5 ft/s to about 10 ft/s. In embodiments, thegasifier is operable at an outlet superficial velocity of gasificationproduct gas comprising entrained particulate heat transfer material inthe range of from about 35 to about 50 ft/s. In embodiments, thegasifier is operable at an operating temperature in the range of fromabout 1000° F. to about 1600° F. In embodiments, the gasifier isoperable at an operating pressure of greater than about 2 psig. Inembodiments, the gasifier is operable at an operating pressure of lessthan about 45 psig. In embodiments, the combustor is configured forfluidization with a combustor fluidization gas having an inlet combustorfluidization gas superficial velocity in the range of from about 15 toabout 25 ft/s. In embodiments, the combustor is operable with an outletflue gas superficial velocity in the range of from about 25 to about 40ft/s. In embodiments, the gasifier comprises a gasifier distributorconfigured to introduce gasifier fluidization gas substantiallyuniformly across the diameter of the gasifier, the combustor comprises acombustor distributor configured to introduce combustor fluidization gassubstantially uniformly across the diameter of the combustor, or both.In embodiments, the combustor is configured to receive particulate heattransfer material at a location at least about 4, 5, or 6 inches abovethe combustor distributor; the gasifier is configured to receive heatedfluidized particulate heat transfer material at a location at leastabout 4, 5, or 6 inches above the gasifier distributor; or both.

In embodiments, the system is operable to provide, from the combustor tothe gasifier, heated fluidized particulate heat transfer material havinga temperature in the range of from about 1400° F. to about 1600° F. Inembodiments, the operating temperature differential between the gasifierand the combustor is less than about 300° F. In embodiments, the systemoptionally comprises at least one seal pot selected from combustor sealpots configured to prevent backflow of material from the combustor intothe at least one gasifier particulate separator, and gasifier seal potsconfigured to prevent backflow of material from the gasifier into the atleast one combustor particulate separator; and at least one componentselected from the group consisting of the gasifier, the combustor, theat least one combustor seal pot, and the at least one gasifier seal potis configured with a dead zone between a distributor and a bottomthereof, such that tramp removal may be performed during operation.

Also disclosed herein is a method comprising: introducing a carbonaceousfeedstock and a heated particulate heat transfer material into agasifier comprising a fluidized bed, whereby at least a portion of thecarbonaceous material is pyrolyzed to produce a gasification product gascomprising hydrogen and carbon monoxide, and wherein the fluidized bedcomprises particulate heat transfer material fluidized by introducing agasifier fluidization gas into the gasifier; removing, from a loweraverage density entrained space region of the gasifier, a gasificationproduct gas comprising, entrained therein, char, particulate heattransfer material, and optionally unreacted carbonaceous feedstock;separating at least one solids product comprising char, particulate heattransfer material, and optionally unreacted carbonaceous material fromthe gasification product gas, providing a particulate-reduced productgas; heating at least a portion of the at least one solids product bypassing same through a combustor, thus producing a heated portion of theat least one solids product and a combustor flue gas, wherein at least aportion of the heat for heating is obtained via combustion of the charin the at least a portion of the at least one solids product; andintroducing at least a portion of the heated portion of the at least onesolids product into the gasifier, providing heat for pyrolysis. Inembodiments, the product comprises Fischer-Tropsch synthesis products,and the method further comprises subjecting at least a portion of thegasification product gas to Fischer-Tropsch synthesis. Subjecting atleast a portion of the gasification product gas to Fischer-Tropschsynthesis may comprise contacting the at least a portion of thegasification product gas with an iron-based Fischer-Tropsch catalyst.The method may further comprise adjusting the molar ratio of hydrogen tocarbon monoxide in the gasification product gas to provide a molar ratioin the range of from about 0.5:1 to about 1.5:1 prior to subjecting theat least a portion of the gasification product gas to Fischer-Tropschsynthesis. Adjusting may comprise subjecting the gasification productgas to partial oxidation. Subjecting at least a portion of thegasification product gas to Fischer-Tropsch synthesis may comprisecontacting the at least a portion of the gasification product gas with acobalt-based Fischer-Tropsch catalyst. Such methods may further compriseadjusting the molar ratio of hydrogen to carbon monoxide in thegasification product gas to provide a molar ratio in the range of fromabout 1.5:1 to about 2.5:1 prior to subjecting the at least a portion ofthe gasification product gas to Fischer-Tropsch synthesis. Subjecting atleast a portion of the gasification product gas to Fischer-Tropschsynthesis may produce non-gaseous Fischer-Tropsch synthesis products, aFischer-Tropsch tailgas, and a spent catalyst product comprising spentFischer-Tropsch catalyst and liquid hydrocarbons. The method maycomprise introducing at least a portion of a Fischer-Tropsch tailgasinto a component selected from the group consisting of the combustor,the gasifier, and seal pots configured to prevent backflow of materialfrom the combustor or from the gasifier. The method may compriseintroducing at least a portion of the spent catalyst product into thegasifier, the combustor, or both.

In embodiments, the method further comprises producing power via atleast a portion of the gasification product gas. The method may compriseproducing power from at least about 10, 20, or 30 volume percent of thegasification product gas, and subjecting at least a portion of theremaining gasification product gas to Fischer-Tropsch synthesis.

In embodiments, the method comprises introducing a supplemental fuelinto the combustor. The supplemental fuel may be selected from the groupconsisting of tar, Fischer-Tropsch wax, Fischer-Tropsch tailgas,upgrader tailgas, refinery tank bottoms, heavy fuel oil, liquid fueloil, and combinations thereof. In embodiments, the method furthercomprises removing tar from the gasification product gas and utilizingat least a portion of the removed tar as supplemental fuel for thecombustor, as carbonaceous feedstock for the gasifier, or both. Themethod may comprise subjecting at least a portion of the gasificationproduct gas to Fischer-Tropsch synthesis, thus producing non-gaseousFischer-Tropsch synthesis products, a Fischer-Tropsch tailgas, and aspent catalyst product comprising spent Fischer-Tropsch catalyst andliquid hydrocarbons, and utilizing at least a portion of theFischer-Tropsch tailgas, at least a portion of the spent catalystproduct, or both as supplemental fuel to the combustor. The method maycomprise subjecting at least a portion of the gasification product gasto Fischer-Tropsch synthesis, thus producing non-gaseous Fischer-Tropschsynthesis products, and subjecting at least a portion of the non-gaseousFischer-Tropsch synthesis products to upgrading, thus producing anupgrader tailgas. In embodiments, the method comprises utilizing atleast a portion of an upgrader tailgas as supplemental fuel for thecombustor.

In embodiments, the method comprises operating the gasifier at agasifier pressure and operating the combustor at a combustor pressurethat is in the range of from about 0 psig to a pressure that is at least2 psig less than the gasifier pressure. In embodiments, the methodcomprises separating heated particulate heat transfer material from thecombustor flue gas. Separating heated particulate heat transfer materialfrom the combustor flue gas may comprise introducing the combustor fluegas into at least one combustor gas/solid separator. In embodiments, theat least one combustor gas/solid separator is operated at a superficialvelocity in the range of from about 70 to about 85 ft/s. In embodiments,(a) separating at least one solids product comprising char, particulateheat transfer material and optionally unreacted carbonaceous materialfrom the gasification product gas comprises introducing at least aportion of the gasification product gas into at least one primarygasifier particulate separator configured to separate particulate heattransfer material from the gasification product gas, thus providing aparticulate-reduced product gas comprising ash, and introducing theparticulate-reduced product gas comprising ash entrained therein into atleast one secondary gasifier particulate separator configured toseparate ash from the particulate-reduced product gas, (b) separatingheated particulate heat transfer material from the combustor flue gascomprises introducing at least a portion of the combustor flue gas intoat least one primary combustor particulate separator configured toseparate particulate heat transfer material from the combustor flue gas,thus providing a particulate-reduced flue gas comprising ash, andintroducing the particulate-reduced flue gas into at least one secondarycombustor particulate separator configured to separate ash from theparticulate-reduced flue gas; or both (a) and (b). Such methods mayfurther comprise introducing at least a portion of the separatedparticulate materials from the primary gasifier particulate separator,the secondary gasifier particulate separator, or both into the combustorfor heating therein. The method may further comprise scrubbing sulfurfrom a gas by contacting the gas with a liquid comprising at least aportion of the separated ash. The gas scrubbed may comprise at least aportion of the gasification product gas.

In embodiments, the method comprises removing more than 99, 99.9, or99.98 weight percent of the particulate heat transfer material from thegasification product gas, from the combustor flue gas, or both. Inembodiments, the method comprises recovering heat from the gasificationproduct gas, from the combustor flue gas, or both. Ash may be removedfrom the gasification product gas, the combustor flue gas, or both,subsequent to heat recovery therefrom. Tar may be removed from thegasification product gas after recovering heat therefrom. Recoveringheat from the gasification gas may reduce the temperature of thegasification product gas to no less than about 900° F., 850° F., 800°F., 750° F. 700° F., 650° F. or 600° F., prior to removing tartherefrom. Recovering heat may comprise heating air via heat transferwith the gasification product gas, the combustor flue gas, or both, andthe method may comprise introducing at least a portion of the heated airinto the combustor.

In embodiments, the method comprises fluidizing the combustor via acombustor fluidization gas. The combustor may be fluidized with acombustor fluidization gas having an inlet combustor fluidization gassuperficial velocity in the range of from about 15 to about 25 ft/s. Thecombustor may be operated with an outlet flue gas superficial velocityin the range of from about 25 to about 40 ft/s. At least a portion ofthe combustor fluidization gas may be introduced via at least onecombustor seal pot configured to prevent backflow of material from thecombustor. In embodiments, at least or about 20% of the combustorfluidization gas needed for fluidization of a bed in the combustor isintroduced via the at least one combustor seal pot.

In embodiments, the method comprises preventing backflow of materialfrom the gasifier via at least one gasifier seal pot, preventingbackflow of material from the combustor via at least one combustor sealpot, or both. In embodiments, the particulate heat transfer material isselected from the group consisting of sand, limestone, and othercalcites or oxides including iron oxide, olivine, and magnesia, alumina,carbides, silica alumina, zeolites, and combinations thereof. The methodmay comprise introducing a catalyst into the gasifier. Such a catalystmay promote tar reforming, thus generating a cleaner gasificationproduct gas than formed in the absence of the catalyst. In embodiments,the catalyst comprises nickel.

In embodiments, the method comprises introducing a sulfur-extractioncomponent, wherein the sulfur extraction component promotes recovery ofsulfur in solid form from the gasification. The sulfur extractioncomponent may comprise calcium oxide. The sulfur extraction componentmay be introduced with the heat transfer material.

In embodiments, the method comprises introducing a carbon dioxideremoval component, the carbon dioxide removal component suitable toconvert carbon dioxide into a solid product that is at least partiallyseparated from the gasification product gas with the at least one solidsproduct. The method may comprise operating the combustor with excessoxygen in the range of from about 0 to about 20 volume percent. Themethod may comprise introducing the carbonaceous feedstock at atemperature in the range of from about −40° F. to about 260° F. Inembodiments, the carbonaceous feedstock comprises at least one materialselected from the group consisting of biomass, RDF, MSW, sewage sludge,coal, Fischer-Tropsch synthesis wax, and combinations thereof. Themethod may comprise introducing a purge gas with or as a part of thecarbonaceous feedstock. The purge gas may comprise at least one gasselected from the group consisting of carbon dioxide, steam, fuel gas,nitrogen, synthesis gas, and combustor flue gas. In embodiments, themethod comprises removing carbon dioxide from the combustor flue gas,the gasification product gas, or both; and utilizing at least a portionof the removed carbon dioxide as purge gas. In embodiments, the methodcomprises operating the combustor at an operating temperature at or nearan inlet thereto for heat transfer material in the range of from about1000° F. to about 1400° F. and an operating temperature at or near anexit thereof to a combustor particulate separator in the range of fromabout 1400° F. to about 1800° F.

The method may comprise removing moisture from a relatively wetcarbonaceous material to provide the carbonaceous feedstock. At least aportion of the heat from the combustor flue gas may be utilized to drythe carbonaceous material. The method may comprise drying a carbonaceousmaterial to a moisture content in the range of from about 10 to about 40weight percent to provide the carbonaceous feedstock. The method maycomprise converting at least about 30, 40, 50, 60, 70, or 80% of thecarbon in the carbonaceous feedstock into gasification product gas. Themethod may comprise introducing the carbonaceous feedstock to thegasifier at a flux of at least or about 2000 lb/h-ft², 2400 lb/h-ft²,2500 lb/h-ft², 3000 lb/h-ft², 3400 lb/h-ft², or 4000 lb/h-ft². Thegasifier fluidization gas may be introduced into the gasifier at asuperficial velocity in the range of from about 0.5 ft/s to about 10ft/s. In embodiments, the method comprises removing the gasificationproduct gas from the gasifier at a superficial velocity in the range offrom about 35 to about 50 ft/s. The gasifier fluidization gas may beselected from the group consisting of steam, flue gas, synthesis gas, LPfuel gas, tailgas (e.g., Fischer-Tropsch tailgas, upgrader tailgas, VSAtailgas, and/or PSA tailgas), gasification product gas, and combinationsthereof. The gasifier may be operated at an operating temperature in therange of from about 1000° F. to about 1600° F. The gasifier may beoperated at an operating pressure of greater than about 2 psig and/orless than about 45 psig.

In embodiments, the gasifier comprises a gasifier distributor configuredto introduce gasifier fluidization gas substantially uniformly acrossthe diameter of the gasifier, the combustor comprises a combustordistributor configured to introduce combustor fluidization gassubstantially uniformly across the diameter of the combustor, or both.The method may comprise introducing particulate heat transfer materialinto the combustor at a location at least about 4, 5, or 6 inches abovea combustor distributor; introducing heated fluidized particulate heattransfer material from the combustor into the gasifier at a location atleast about 4, 5, or 6 inches above a gasifier distributor; or both. Atleast a portion of the heated portion of the at least one solids productmay be introduced into the gasifier at a temperature in the range offrom about 1400° F. to about 1600° F. An operating temperaturedifferential of less than about 350° F., 325° F., 300° F., 275° F., or250° F. may be maintained between the gasifier and the combustor.

The foregoing has outlined rather broadly the features and technicaladvantages of the invention in order that the detailed description ofthe invention that follows may be better understood. Additional featuresand advantages of the invention will be described hereinafter that formthe subject of the claims of the invention. It should be appreciated bythose skilled in the art that the conception and the specificembodiments disclosed may be readily utilized as a basis for modifyingor designing other structures for carrying out the same purposes of theinvention. It should also be realized by those skilled in the art thatsuch equivalent constructions do not depart from the spirit and scope ofthe invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of theinvention, reference will now be made to the accompanying drawings inwhich:

FIG. 1 is schematic of a gasification system according to thisdisclosure; and

FIG. 2 is a schematic of an integrated system comprising a gasificationsystem according to this disclosure integrated with Fischer-Tropschsynthesis and power production.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. This document does not intendto distinguish between components that differ in name but not function.

The terms ‘pyrolyzer’ and ‘gasifier’ are used interchangeably herein torefer to a reactor configured for endothermal pyrolysis.

DETAILED DESCRIPTION

Overall Dual Fluidized Bed (DFB) System.

Herein disclosed are a dual fluidized bed gasification system, novelcomponents thereof, and methods of gasification using same. Disclosedherein are a combustor, a pyrolyzer, combustor seal pot, gasifier sealpot, primary gasifier separator (e.g., heat transfer material, HTM,cyclone), secondary gasifier separator (e.g., ash cyclone), combustorseparators (e.g., primary and/or secondary cyclones), and a systemcomprising a combination of one or more of these components andoptionally comprising downstream apparatus configured for the productionof chemicals, fuels, and/or power from the gas produced in the gasifier.

The disclosed method comprises introducing inlet gas at a low gasvelocity to fluidize a high average density bed in a gasifier/pyrolysisvessel. The high average density bed may comprise a relatively densefluidized bed in a lower region thereof, the relatively dense fluidizedbed containing a circulating heated relatively fine and inertparticulate heat transfer material. Carbonaceous material is introducedinto the lower region at a relatively high rate and endothermalpyrolysis of the carbonaceous material is accomplished by means of acirculating heated inert material, producing a gasifier product gascomprising synthesis gas (i.e. comprising hydrogen and carbon monoxide).In embodiments, in an upper region of the pyrolyzer is a lower averagedensity entrained space region containing an entrained mixturecomprising inert solid, particulate heat transfer material, char,unreacted carbonaceous material and product gas. The entrained mixtureis removed from the gasifier to one or more separators, such as acyclone, wherein solids (heat transfer particles, char and/or unreactedcarbonaceous material) are separated from the gasification product gas.At least a portion of the removed solids is returned to the pyrolyzerafter reheating to a desired temperature via passage through anexothermic reaction zone of an external combustor.

FIG. 1 is a schematic of a dual fluidized bed (or ‘DFB’) gasificationsystem 10 according to this disclosure. DFB gasification system 10comprises a gasifier 20 (also referred to herein as a ‘pyrolyzer’) thatis fluidly connected with a combustor 30, whereby heat lost duringendothermic gasification in gasifier/pyrolyzer 20 can be supplied viaexothermic combustion in combustor 30, as discussed further hereinbelow.DFB gasification system 10 further comprises at least one combustor sealpot 70 and at least one gasifier seal pot 80. Pyrolyzer 20 is operablefor removal therefrom of a circulating particulate phase and char byentrainment in gasifier product gas. Separation of solid, entrainedparticulates comprising particulate heat transfer material and char fromthe gasification product gas, can be accomplished by gas/solidseparators, such as conventional cyclone(s). In embodiments,substantially all system solids are elutriated by the herein disclosedmethod despite the use of what are generally considered to be low inletgasifier fluidization gas velocities. The DFB gasification system thusfurther comprises one or more gasifier particulate separator (e.g., oneor more gasifier cyclones) and one or more combustor particulateseparator (e.g., one or more combustor cyclones). In the embodiment ofFIG. 1, DFB gasification system 10 comprises primary gasifier cyclones40 and secondary gasifier cyclones 50 and combustor cyclones 60. Each ofthese components will be discussed in more detail hereinbelow.

Circulating between the gasifier and the combustor is a heat transfermaterial (HTM). The heat transfer material is relatively inert comparedto the carbonaceous feed material being gasified. In embodiments, theheat transfer material is selected from the group consisting of sand,limestone, and other calcites or oxides such as iron oxide, olivine,magnesia (MgO), attrition resistant alumina, carbides, silica aluminas,attrition resistant zeolites, and combinations thereof. The heattransfer material is heated by passage through an exothermic reactionzone of an external combustor. In embodiments, the heat transfermaterial may participate as a reactant or catalytic agent, thus‘relatively inert’ as used herein with reference to the heat transfermaterial is as a comparison to the carbonaceous materials and is notused herein in a strict sense. For example, in coal gasification,limestone may serve as a means for capturing sulfur to reduce sulfateemissions. Similarly, limestone may serve to catalytically crack tar inthe gasifier. In embodiments, the gasifier may be considered a catalyticgasifier, and a catalyst may be introduced with or as a component of theparticulate heat transfer material. For example, in embodiments, anickel catalyst is introduced along with other heat transfer material(e.g., olivine or other heat transfer material) to promote reforming oftars, thus generating a ‘clean’ synthesis gas that exits the gasifier.The clean synthesis gas may be an essentially tar-free synthesis gas. Inembodiments, an amount of nickel catalyst (e.g., about 5, 10, 15, or 20weight percent nickel) is circulated along with other heat transfermaterials.

The heat transfer material may have an average particle size in therange of from about 1 μm to about 100 mm, from about 1 μm to about 1 mm,or from about 5 μm to about 300 μm. The heat transfer material may havean average density in the range of from about 50 lb/ft³ (0.8 g/cm³) toabout 500 lb/ft³ (8 g/cm³), from about 50 lb/ft³ (0.8 g/cm³) to about300 lb/ft³ (4.8 g/cm³), or from about 100 lb/ft³ (1.6 g/cm³) to about300 lb/ft³ (4.8 g/cm³).

In embodiments, equilibrium is pushed toward the formation of hydrogenand carbon monoxide during pyrolysis via, for example, the incorporationof a material that effectively removes carbon dioxide. For example, NaOHmay be introduced into the system (e.g., to or with the heat transfermaterial, to gasifier 20, to combustor 30, or elsewhere in the system)to produce Na₂CO₃, and/or CaO injection may be utilized to absorb CO₂,forming CaCO₃ which may later be separated into CO₂ and CaO which may berecycled into the system. The NaOH and/or CaO may be injected intogasifier or pyrolizer 20. Addition of such carbon dioxide reducingmaterial may serve to increase the amount of synthesis gas produced (andthus available for downstream processes such as, without limitation,Fischer-Tropsch synthesis and non-Fischer-Tropsch chemical and/or fuelproduction), and/or may serve to increase the Wobbe number of thegasifier product gas for downstream power production. Such or furtheradditional materials may also be utilized to adjust the ash fusiontemperature of the carbonaceous feed materials within the gasifier. Aswith the optional carbon dioxide reducing materials, such ash fusionadjustment material(s) may be incorporated via addition with or to thefeed, with or to the heat transfer media, to gasifier 20, to combustor30, and/or elsewhere. In embodiments, the additional material(s) areadded with or to the feed to the gasifier. In embodiments, theadditional material(s) are added with or to the heat transfer media.

Reactor/Gasifier/Pyrolyzer 20.

Pyrolyzer 20 is a reactor comprising a fluid-bed of heat transfermaterial at the reactor base, and is operated at feed rates sufficientlyhigh to generate enough gasifier product gas to promote circulation ofheat transfer material and gasified char, for example, by entrainment.The gasifier may be a hybrid with an entrained zone above a fluidizedbed gasifier, as described in U.S. Pat. No. 4,828,581, which is herebyincorporated herein by reference in its entirety for all purposes notcontrary to this disclosure.

In embodiments, gasifier/pyrolyzer 20 is an annular shaped vesselcomprising a conventional gas distribution plate near the bottom andcomprising inlets for feed material(s), heat transfer material(s), andfluidizing gas. The gasifier vessel comprises an exit at or near the topthereof and is fluidly connected thereby (e.g. via gasifier outlet line114) to one or more separators from which gasification product gas isdischarged and solids are recycled to the bottom of the gasifier via anexternal, exothermic combustor operable to reheat the separated, heattransfer material. The gasifier operates with a recirculatingparticulate phase (heat transfer material) and at inlet gas velocitiesin the range sufficient to fluidize the heat transfer material, asfurther discussed hereinbelow.

Gasifier Feed.

As indicated in the embodiment of FIG. 1, the inlets for feed (e.g. vialine 90) and recirculating heat transfer material (e.g. via ‘hot’circulation line 35) are located at or near the base of gasifier 20, andmay be proximate the pyrolyzer gas distributor 95. The feed may beselected from the group consisting of biomass, RDF, MSW, sewage sludge,and combinations thereof. In embodiments, the feed comprises biomass. Itis envisaged that coal may be added to the gasifier if it is suitablecoal, and this depends on the ash fusion temperature. Refinery tankbottoms, heavy fuel oil, etc, which may, in embodiments, be contaminatedwith small solids may be introduced into the gasifier and/or thecombustor, so long as the ash fusion temperature therein is notadversely affected. In embodiments, petcoke is ground to a size in therange suitable to ensure volatilization within the pyrolyzer. Inembodiments, petcoke is introduced into the pyrolyzer as a component ofthe carbonaceous feedstock. In embodiments, the gasifier feed furthercomprises Fischer-Tropsch synthesis products (e.g., Fischer-Tropsch wax)and/or spent catalyst (e.g., recycled spent catalyst in product wax). Inembodiments, Fischer-Tropsch synthesis products are produced downstreamand a portion of the Fischer-Tropsch product(s) (e.g., spentFischer-Tropsch wax) that will crack under the operating conditionstherein is recycled as feed/fuel to the gasifier.

The gasifier feed may be introduced thereto via any suitable means knownto one of skill in the art. The feed may be fed to the gasifier using awater cooled rotary screw. The feed may be substantially solid and maybe fed utilizing a screw feeder or a ram system. In embodiments, thefeed is introduced into the gasifier as a solid extrudate. Inembodiments, dual feed screws are utilized and operation is alternatedtherebetween, thus ensuring continuous feeding.

As indicated in FIG. 1, a gasifier feed inlet line 90 may be configuredto provide an angle β between the feed inlet line 90 and gasifier vessel20. The feed inlet angle β may be in the range of from about 5 to about20 degrees or from about 10 to about 15 degrees such that the feed flowssubstantially uniformly into (i.e. across the cross section thereof) ofpyrolyzer 20. In this manner, feed isn't limited to one side of thepyrolyzer, for example. A purge gas may also be introduced (e.g. vialine 91) with the feed (for example, from a lockhopper) via the feedinlet to maintain a desired pressure and/or to aid in feeding the feedto the pyrolyzer. In embodiments, the purge gas is selected from thegroup consisting of carbon dioxide, steam, fuel gas, nitrogen, synthesisgas, flue gas from the combustor and combinations thereof. Inembodiments, the purge gas comprises nitrogen. In embodiments, the feedis not purged. If CO₂ recovery is present, for example downstream in thesystem, it may be desirable for the feed purge gas to be or to comprisecarbon dioxide.

In embodiments, the gasifier feed is pressurized. The carbonaceous feedmaterial may be fed to the gasifier at a pressure in the range of fromabout 0 to about 40 psig. A dryer may be utilized to dry the feed and/ormay be operated at a pressure, thus providing the feed material to thegasifier at a desired pressure and/or moisture content. The feed may bedried prior to introduction into the gasifier, and may be introduced hot(e.g., at a temperature of greater than room temperature). Inembodiments, the feed is cold (e.g., at a temperature of less than roomtemperature). The feed may be introduced into the gasifier at atemperature in the range of from about −40 to about 260° F. Inembodiments, the feed is at a temperature in the range of from −40 toabout 250° F. In embodiments, the feed is at ambient temperature. Inembodiments, the feed is at ambient temperature. In embodiments, a feedmaterial is comminuted prior to introduction into the gasifier. Inembodiments, a feed material is preheated and/or comminuted (e.g.,chipped) prior to introduction into the gasifier.

Optimization of Gasifier Feed Drying to Control H₂:CO Ratio in ProductSynthesis Gas.

In embodiments, the moisture content of the feed is in the range of fromabout 5% to about 60%. In embodiments, the feed has a moisture contentof greater than about 10, 20, 30, or 40 wt %. In embodiments, the feedhas a moisture content of less than about 10, 20, 30, or 40 wt %. Inembodiments, the moisture content of the feed is in the range of fromabout 20 to about 30 wt %. In embodiments, the moisture content of thefeed is in the range of from about 20 to about 25 wt %.

In embodiments, more drying of the feed material may be desired/utilizedto provide syngas (via, for example, feed drying, gasification and/orpartial oxidation) at a molar ratio of H₂/CO suitable for downstreamFischer-Tropsch synthesis in the presence of an iron catalyst (i.e.about 1:1). In embodiments, less drying may be desired/utilized, forexample, to provide a synthesis gas having a molar ratio of H₂/COsuitable for downstream Fischer-Tropsch synthesis in the presence of acobalt catalyst (i.e. about 2).

Energy Integration for Dryer.

A dryer 155 may be configured to reduce the moisture content of a ‘wet’carbonaceous feed material (e.g. biomass, BM). Carbonaceous feedmaterial (e.g. biomass) may be introduced into dryer 155 viacarbonaceous feed material inlet line BM, drying fluid (e.g. ‘hot’combustor flue gas) may be introduced into dryer 155 via drying agentinlet line 156, and/or dryer exhaust may be extracted from dryer 155 viadryer exhaust line 157. In embodiments, at least a portion of the hotcombustor flue gas (described further hereinbelow) is utilized to dry agasifier feed prior to introduction into gasifier 20. In suchembodiments, combustor flue gas outlet line 112 may be fluidly connectedwith dryer 155, for example, via drying agent inlet line 156.

In embodiments, the feed rate (flux) of carbonaceous material to thegasifier is greater than or equal to about 2000, 2500, 3000, 3400, 3500,lb/h/ft², 4000, or 4200 lb/h/ft². The design may allow for a superficialvelocity at the outlet (top) of the gasifier in the range of 40-45 ft/s(assuming a certain carbon conversion/volatilization/expansion). Inembodiments, the carbon conversion is in the range of from about 0 toabout 100%. In embodiments, the carbon conversion is in the range offrom about 30 to about 80%. The gasifier vessel size, i.e. the diameterthereof, may be selected based on a desired outlet velocity.

Gasifier fluidization gas may be fed to the bottom of gasifier 20 (forexample, via a distributor 95) at a superficial velocity in the range offrom about 0.5 ft/s to about 10 ft/s, from about 0.8 ft/s to about 8ft/s, or from about 0.8 ft/s to about 7 ft/s. In embodiments, thepyrolyzer fluidization gas (e.g., steam) inlet velocity is greater than,less than, or equal to about 1, 2, 3, 4, 5, 6, 7 or 8 ft/s. Inembodiments, a gasifier fluidization gas superficial velocity of atleast or about 5, 6, 7, or 8 ft/s is utilized during startup.

The fluidization gas introduced into the gasifier via line 141 and 141 a(and optionally introduced into circulation line 35 via line 141 d) maybe selected from the group consisting of steam, flue gas, synthesis gas,LP fuel gas, tailgas (e.g., Fischer-Tropsch tailgas, upgrader tailgas,VSA tailgas, and/or PSA tailgas) and combinations thereof. Inembodiments, the gasifier fluidization gas comprises Fischer-Tropschtailgas. In embodiments, the gasifier fluidization gas comprisesupgrader tailgas. By utilizing upgrader tailgas, additional sulfurremoval may be effected, as the upgrader tailgas may comprise sulfur.

In embodiments, the pyrolyzer fluidization gas comprises PSA tailgas.Such embodiments may provide substantial hydrogen and may be mostsuitable for subsequent utilization of the product gas in downstreamprocesses for which higher molar ratios of hydrogen to carbon monoxideis desirable. For example, higher molar ratios of hydrogen to carbonmonoxide may be desirable for downstream processes such as a nickel dualfluidized bed gasification system (for which H₂/CO ratio of about 1.8:1to about 2:1 may be desired). Such a dual fluidized bed (DFB) gasifieris disclosed, for Example, in U.S. patent application Ser. No.12/691,297 filed Jan. 21, 2010, the disclosure of which is herebyincorporated herein for all purposes not contrary to this disclosure.Utilization of PSA tailgas for gasifier fluidization gas may be lessdesirable for subsequent utilization of the gas for POx (for which H₂/COratios closer to or about 1:1 may be more suited), as the hydrogen maybe undesirably high. In embodiments, the gasification product gas isdried (for example, in a burner) to a moisture content of less than adesired amount (e.g., less than about 10, 11, 12, 13, 14, or 15 percent)in order to provide a suitable composition (e.g., H₂/CO molar ratio) fordownstream processing (e.g., for downstream POx). In embodiments, acombination of feed drying, DFB gasification and POx is utilized toprovide a synthesis gas suitable for downstream Fischer-Tropschsynthesis utilizing a cobalt catalyst.

The temperature at or near the top of the gasifier (e.g., proximateentrained product removal therefrom) may be in the range of from about1000° F. to about 1600° F., from about 1100° F. to about 1600° F., fromabout 1200° F. to about 1600° F., from about 1000° F. to about 1500° F.,from about 1100° F. to about 1500° F., from about 1200° F. to about1500° F., from about 1000° F. to about 1400° F., from about 1100° F. toabout 1400° F., from about 1200° F. to about 1400° F., from about 1200°F. to about 1450° F., from about 1200° F. to about 1350° F., from about1250° F. to about 1350° F., from about 1300° F. to about 1350° F. orabout 1350° F.

In embodiments, the gasifier pressure is greater than about 2 psig. Inembodiments, the gasifier pressure is less than or equal to about 45psig. In embodiments, the gasifier pressure is in the range of fromabout 2 psig to about 45 psig.

Heat transfer material is introduced, via ‘hot’ circulation line 35,into a lower region of the gasifier. The heat transfer material may beintroduced approximately opposite introduction of the gasifier feedmaterial. To maintain suitable flow, the HTM inlet may be at an angle γin the range of from about 20 degrees to about 90 degrees, or at anangle γ of greater than or about 20, 30, 40, 50, or 60 degrees. The heattransfer material may be introduced at a temperature in the range offrom about 1400° F. to about 1600° F., from about 1450° F. to about1600° F., from about 1525° F. to about 1575° F., or about 1550° F.

In embodiments, the pyrolyzer comprises a gas distributor 95. Inembodiments, the heat transfer material is introduced to pyrolyzer 20 ata location at least 4, 5, 6, 7, 8, 9 or 10 inches above pyrolyzer gasdistributor 95. The heat transfer material may be introduced at aposition in the range of from about 4 to about 10 inches, or from about4 to about 6 inches above the distributor. In embodiments, thedistributor is operable to provide a gas flow rate of at least or about4, 5, 6, 7, 8, 9, or 10 ft/s, for example, during startup. The gasifierdistributor (and/or a distributor in a combustor seal pot, a gasifierseal pot, and/or the combustor) may comprise a ring distributor, a pipedistributor, a Christmas tree distributor, or other suitable distributordesign known in the art. In embodiments, the distributor comprises apipe distributor that may be loaded through a side of the vessel forease of nozzle replacement thereon (generally suitable in embodiments inwhich the running pressure is less than 12 or 15 psig inclusive).Distributors with fewer inlets (e.g., Christmas tree distributors and/orring distributors) may be more desirable for higher pressureapplications.

In embodiments, the temperature differential between the gasifier andthe combustor (i.e. T_(C)-T_(G)) is maintained at less than about 250°F., 260° F., 270° F., 280° F., 290° F., 300° F., 310° F., 320° F., 330°F., 340° F., or 350° F., or is maintained at a temperature within anyrange therebetween. If T_(C)-T_(G) is greater than about 300° F., sandor other elevated temperature heat transfer material may be added to thesystem.

Tramp Removal System.

Gasifier distributor 95 may be positioned 3 to 6 feet above therefractory bottom. In embodiments, the distributor is positioned atleast 3, 4, 5, or at least 6 feet above the refractory bottom. Below thedistributor is thus created a dead space or ‘dead zone’ 96, as indicated(not to scale) in the embodiment of FIG. 1. Dead zone 96 is locatedbetween the distributor and the bottom of the vessel. In embodiments,such a dead zone may be designed to facilitate removal of heat transfermaterial from below a distributor. Any materials that are too heavy tofluidize may settle below the distributor of a system component, thuscreating a heat sink area. Because there may be little or nofluidization below the distributor, heat transfer material may becometrapped below the distributor and cool (e.g., to less than 1550° F. orto below another HTM inlet gasifier temperature). The bottom of thegasifier (or another component such as a combustor seal pot 70, agasifier seal pot 80, or combustor 30) may be designed with two valvesand a pipe whereby tramp removal may be effected during operation. Thedesign of such a lock hopper allowing for online removal of heattransfer material from the dead zone may desirably eliminate the needfor shutdown during tramp removal. As indicated, such a tramp removalsystem may also be utilized on the combustor, the CSP, the GSP, or anycombination of vessels, whereby materials may be removed therefromwithout taking the system(s) offline.

Gasifier Cyclones.

The herein disclosed DFB system comprises one or more gas/solidseparator (e.g., one or more cyclone) on the gasifier outlet line 114.The system may comprise primary gasifier particulate separator(s) 40 andsecondary gasifier particulate separator(s) 50 (e.g., primary andsecondary gasifier cyclones). Particulate-reduced gasification productgas extracted from primary gasifier particulate separator 40 may beintroduced into secondary gasifier particulate separator 50 via line 114a. Solids (e.g. char, unreacted carbonaceous material, and/or HTM)extracted from the gasification product gas via primary gasifierparticulate separator 40 may be introduced into combustor seal pot 70,for example, via dipleg 41. Particulate-reduced gasification product gasextracted from secondary gasifier particulate separator 50 may beintroduced into downstream apparatus 100 via line 114 b. Solids (e.g.char, unreacted carbonaceous material, and/or HTM) extracted from thegasification product gas via secondary gasifier particulate separator 50may be introduced into combustor seal pot 70, for example, via dipleg51.

In embodiments, the gasifier separators are operable/configured toprovide a HTM removal efficiency of at least or about 98, 99, 99.9, or99.99%. In embodiments, the primary gasifier separators 40 are operableto remove at least or about 99.99% of the heat transfer material from agas introduced thereto. Higher removal of heat transfer material isgenerally desirable, as the cost of makeup particulate heat transfermaterial and the cost of heating same to operation temperature areconsiderable. The secondary gasifier particulate separator(s) 50 (e.g.,cyclones) may be configured to remove at least about 80, 85, 90 or 95%of the char (and/or ash) in the gasifier product gas introduced theretovia line 114 a. In embodiments, the secondary gasifier separators areoperable to remove at least about 95% of the ash and/or char introducedthereto. There may be some (desirably minimal) amount of recycle ash. Asnoted hereinabove, solids extracted via the primary gasifierseparator(s) 40 and/or secondary gasifier particulate separator(s) 50may be introduced into combustor seal pot 70 via diplegs 41 and 51respectively. The exit from the gasifier to the gasifier primarycyclones may comprise a 90 degree flange.

Syngas Heat Recovery.

The product synthesis gas exiting the gasifier separators may beutilized for heat recovery in certain embodiments. In embodiments, thesynthesis gas is not utilized for heat recovery. In embodiments, no heatrecovery is incorporated on the syngas and the DFB gasification systemfurther comprises a POx unit, a nickel dual fluidized bed gasifierand/or a boiler downstream of the gasifier separator(s). It is envisagedthat heat recovery apparatus may be positioned between primary andsecondary separators. When utilized for heat recovery, the temperatureof the synthesis gas may be maintained at a temperature of at least 600°F., at least 650° F., at least 700° F., at least 750° F. or at least800° F. after heat recovery. For example, maintenance of a temperatureof greater than 650° F., 700° F., 750° F., 800° F., 850° F., or 900° F.may be desirable when heat recovery is upstream of tar removal (forexample, to prevent condensation of tars). In embodiments, the synthesisgas is maintained at a temperature in the range of from about 650° F. toabout 800° F. during heat recovery. In embodiments, the system comprisesa steam superheater and optionally there-following a waste heat boileror waste heat superheater downstream of the gasifier separators for heatrecovery from the hot gasification gas comprising syngas and productionof steam. In embodiments, the system comprises an air preheater for heatrecovery from the hot synthesis gas. In embodiments, the systemcomprises a boiler feedwater (BFW) preheater for heat recovery from thehot synthesis gas. The system may comprise an air preheater, (forexample to preheat air for introduction into the combustor, as theintroduction of hotter air into the combustor may be desirable). Thesystem may comprise any other suitable apparatus known to those of skillin the art for heat recovery.

Combustor/CSP.

The system comprises a combustor configured to heat the heat transfermaterial separated via one or more separators (e.g., cyclones) from thegasification product comprising entrained materials extracted from thepyrolyzer. The combustor may be any type of combustor known in the art,such as, but without limitation, fluidized, entrained, and/ornon-fluidized combustors. ‘Cold’ circulation line 25 is configured tointroduce ‘cold’ HTM into combustor 30, while ‘hot’ circulation line 35is configured to introduce ‘hot’ HTM into gasifier 20.

Referring now to FIG. 1, combustor 30 is associated with a combustorseal pot 70 (CSP) configured to prevent backflow of materials into thegasifier cyclone(s) 40, 50; and one or more combustor cyclones 60configured to remove particulates from the combustor flue gas.

In embodiments, air is fed into the bottom of combustor 30 (e.g. vialine 121) and steam is fed into CSP 70. The steam feed rate may be about4000 lb/h (for a plant operating at about 500 dry tons/day, forexample). The steam passes through and exits combustor cyclone 60. Thecyclone efficiency is dramatically affected by the superficial velocitythereto. The higher the superficial velocity, the better the cycloneefficiency. If the ACFM (actual cubic feet per minute) can be reduced,the cyclone efficiency may be improved (based on more solids per cubicfoot). Thus, in embodiments, air is fed into CSP 70, rather than steam.In embodiments, 20-25% of the fluidization gas (e.g., air) for combustor30 is introduced into or via CSP 70, for example, via line 141 b, and/orinto circulation line 25, for example via line 141 c. In embodiments,combustion air, rather than steam, is fed into CSP 70, such that heat isnot removed from combustor 30 due to the flow of steam therethrough andthe downstream combustor separator(s)/cyclone(s) 60 and/or thedownstream gasifier 20 may be incrementally smaller in size. That is,the introduction of air (e.g., at about 1000° F.), rather than theintroduction of (e.g., 550° F.) steam into CSP 70 (which is heatedtherein to, for example, about 1800° F.) may serve to reduce the amountof steam in gasification system 10. This may allow the downstreamvessel(s) to be smaller. When air is introduced into CSP 70, partialcombustion of char may occur in the seal pot with air (rather thansteam) and the downstream combustor cyclone 60 and/or gasifier 20 may besmaller. Accordingly, in embodiments the combustor is reduced in size byintroduction of a portion of the combustor fluidization gas into CSP 70.For example, if the desired fluidization velocity at the top (e.g.,proximate the flue gas exit) of the combustor is 30-35 ft/s, only about75-80% (i.e. about 20 feet/s) may need to be introduced into the bottomof the combustor because 20-25% of the fluidization gas may beintroduced into or via the CSP. Thus, the combustor size may be reduced.Another benefit of introducing combustor fluidization gas via the CSP isthat the combustor cyclone(s) can be incrementally smaller or beoperated more efficiently. Also, nitrogen in the air can be heated andthermal efficiency gained by eliminating or reducing the need forsuperheating steam (e.g., at 4000 lb/h of steam).

In embodiments, the fluidization gas for one or more of the gasifier 20,the gasifier seal pot 80, the combustor seal pot 70, and the combustor30 comprises LP fuel gas. The fluidization gas in combustor 30 maycomprise primarily air. The gas feed rate to the combustor may begreater than, less than, or about 10, 15, 20, 25, 30, or 35 feet/s incertain embodiments.

The slope from combustor seal pot 70 into combustor 30 provides angle α,such that the heat transfer media (e.g., sand), air and flue gas willflow over and back into the combustor. The inlet flow of fluidizationgas into the combustor may be determined by the heat transfer material.The inlet fluidization velocity is at least that amount sufficient tofluidize the heat transfer media within combustor 30. In embodiments,the inlet velocity to the combustor is greater than or about 10, 15, 20,25, or 30 ft/s. In embodiments, the inlet velocity of fluidization gasinto the bottom of the combustor is in the range of from about 15 toabout 35 ft/s, from about 20 to about 35 ft/s, or from about 20 to about30 ft/s. At higher elevations in the combustor, flue gas is created.This limits the suitable rate for introduction of fluidization gas intothe combustor.

In embodiments, the combustor is operated in entrained flow mode. Inembodiments, the combustor is operated in transport bed mode. Inembodiments, the combustor is operated in choke flow mode. The bottom ofthe combustor (for example, at or near the inlet of circulating heattransfer media from the gasifier) may be operated at approximately 1100°F., 1200° F., 1300° F., or 1400° F., and the exit of the combustor (ator near the top thereof; for example, at or near the exit of materialsto cyclone(s)) may be operated at approximately 1400° F., 1500° F., or1600° F. Thus, the actual cubic feet of gas present increases withelevation in the combustor (due to combustion of the char and/orsupplemental fuel). In embodiments, excess air flow is returned to thecombustor.

The fluidization gas for the combustor may be or may comprise oxygen inair, oxygen-enriched air, substantially pure oxygen, for example, from avacuum swing adsorption unit (VSA) or a pressure swing adsorption unit(PSA), oxygen from a cryogenic distillation unit, oxygen from apipeline, or a combination thereof. The use of oxygen or oxygen-enrichedair may allow for a reduction in vessel size, however, the ash fusiontemperature must be considered. The higher the O₂ concentration in thecombustor feed, the higher the temperature of combustion. The oxygenconcentration is kept at a value which maintains a combustiontemperature less than the ash fusion temperature of the feed. Thus, themaximum oxygen concentration fed into the combustor can be selected bydetermining the ash fusion temperature of the specific feed utilized. Inembodiments, the fluidization gas fed to the bottom of the combustorcomprises from about 20 to about 100 mole percent oxygen. Inembodiments, the fluidization gas comprises about 20 mole percent oxygen(e.g., air). In embodiments, the fluidization gas comprisessubstantially pure oxygen (limited by the ash fusion properties of thechar, supplemental fuel and heat transfer material fed thereto). Inembodiments, the combustor fluidization gas comprises PSA tailgas.

The combustor may be designed for operation with about 10 volume percentexcess oxygen in the combustion offgas. In embodiments, the combustor isoperable with excess oxygen in the range of from about 0 to about 20volume percent, from about 1 to about 14 volume percent, or from about 2to about 10 volume percent excess O₂. In embodiments, the amount ofexcess O₂ fed to the combustor is greater than 1 volume percent and/orless than 14 volume percent. Desirably, enough excess air is providedthat partial oxidation mode is avoided. In embodiments, the DFBgasification system is operable with excess O₂ to the combustor in therange of greater than 1 to less than 10 and the flue gas comprises lessthan 15, 10, or 7 ppm CO. In embodiments, oxygen is utilized to producemore steam. In embodiments, for example, when the hot flue gas will beintroduced into a second combustor (for example, without limitation,into the combustor of a second dual fluidized bed (DFB) gasifier asdisclosed, for example, in U.S. patent application Ser. No. 12/691,297filed Jan. 21, 2010, the disclosure of which is hereby incorporatedherein for all purposes not contrary to this disclosure), the amount ofexcess oxygen may be in the range of from about 5 to about 25 percent,or may be greater than about 5, 10, 15, 20, or 25%, providing oxygen fora downstream combustor. In embodiments in which steam may be sold atvalue, more excess O₂ may be utilized to produce more steam forsale/use. In embodiments, a CO-rich, nitrogen-rich flue gas is producedby operation of combustor 30 of the herein disclosed DFB gasificationsystem at excess oxygen of greater than 7, 10 or 15%.

Supplemental Fuels to the Combustor.

In embodiments, supplemental fuels may be introduced into combustor 30,for example, via supplemental fuel inlet line 122. The supplementalfuels may be carbonaceous or non-carbonaceous waste streams and may begaseous, liquid, and/or solid. For example, in embodiments, spentFischer-Tropsch wax (which may contain up to about 5, 10, 15, 20, 25, or30 weight percent catalyst) may be introduced into the combustor (and/orthe gasifier, as discussed further hereinbelow). In embodiments,Fischer-Tropsch wax is produced downstream and spent Fischer-Tropsch waxis recycled as fuel to the combustor. As discussed further hereinbelow,such spent wax can alternatively or additionally also be introduced intothe gasifier, providing that it will crack under the operatingconditions therein. In embodiments, petcoke is fed to the combustor, asa fuel source.

In embodiments, a hydrocarbon laden stream (e.g., tar that may resultfrom a tar removal system) is introduced into the combustor for recoveryof the heating value thereof. The tar may be obtained from any tarremoval apparatus known in the art, for example from a liquid absorbersuch as but not limited to an OLGA (e.g., a Dahlman OLGA) unit. Suchremoved tars comprise heavy hydrocarbons which may be reused as acomponent of feed/fuel to combustor 30. In embodiments, tailgas (e.g.,Fischer-Tropsch tailgas, PSA tailgas, VSA tailgas and/or upgradertailgas) is utilized as a fuel to the combustor.

In embodiments, a liquid feed such as, but not limited to, refinery tankbottoms, heavy fuel oil, liquid fuel oil (LFO), Fischer-Tropsch tarand/or another material (e.g., waste material) having a heating value,is introduced into the combustor. Nozzles may be positioned above thedipleg for introduction of such liquid material(s) into the combustor.This may help the liquid flow into the downleg and avoid production ofcold spots on the refractory. In this manner, circulating heat transfermaterial may be utilized to circulate the liquid and the liquid may becarried into the combustor via the combustor fluidization gas (e.g.,air).

Combustor 30 may be fabricated with a 2-4 inch thick hard facerefractory. In embodiments, the combustor has at least 2″ hard face. Inembodiments, combustor 30 has at least 3″ hard face. In embodiments(e.g., in lower insulation embodiments), the combustor may comprise ahard face refractory with an insulating layer surrounding the hard face.The insulating layer may be thicker than 2 inches. In embodiments, theinsulation layer is thicker than the hardface layer. The hardface layermay have a higher thermal conductivity and durability than theinsulating layer.

In embodiments, the combustor is substantially cylindrical. Inembodiments, the combustor is non-cylindrical. In embodiments, thecombustor is conical at the bottom and/or the top. In embodiments, thecombustor is conical at the bottom, for example, when the fluidizationgas for the combustor comprises a high concentration of oxygen. Inembodiments, the combustor comprises a conical disengaging section atthe top (however, this embodiment may undesirably reduce the superficialvelocity into downstream combustor gas/solid separator(s)). Inembodiments, the outlet of the combustor comprises channels configuredfor recycle of heat transfer material to the fluidized bed of thecombustor and reduce particulate loading in primary separator(s). Inembodiments, the outlet of the combustor is corrugated to reduceparticulate loading on primary cyclone(s).

In embodiments, the combustor is pressurized. The combustor may beoperable at a pressure of greater than 0 psig to a pressure that is atleast 2 psig less than the operating pressure of the gasifier. That is,in order to maintain continuous flow of materials from the combustorback into the gasifier, the pressure of the combustor, P_(C), at theinlet to the combustor which may be measured by a pressure gauge locatedproximate the flue gas exit, is less than the gasifier/pyrolyzerpressure, P_(G). The pressure at the HTM outlet of the combustor,P_(C,BOTTOM) (which must be greater than P_(G)), equals the sum of thepressure, P_(C), at the top of the combustor and the head of pressureprovided by the material in the combustor. The head of pressure providedby the heat transfer material/gas mixture within the combustor is equalto ρ_(C)gh, where ρ_(C) is the average density of the material (e.g.,the fluidized bed of heat transfer material) within the combustor, g isthe gravitational acceleration, and h is the height of the ‘bed’ ofmaterial within the combustor. The height of material (e.g., heattransfer material such as sand, and other components such as char andetc.) within the combustor is adjusted to ensure flow of materials backto the gasifier.

Thus, P_(C, BOTTOM) which equals P_(C)+ρ_(C)gΔh must be greater than thepressure of the gasifier, P_(G). The heights and relationships betweenthe combustor and gasifier are selected such that adequate pressure isprovided to maintain continuous flow from the combustor to the gasifierand back.

In embodiments, the operating pressure of the combustor, P_(C), is up toor about 40, 45, or 50 psig. In embodiments, based on 30-40 ft/s designcriteria for gas velocity into the combustor, the maximum operatingpressure of the combustor is about 45 psig. In embodiments, if theoperating pressure of the combustor is increased, then the pressureenergy can be recovered by the use of an expander. Thus, in embodiments,one or more expander is positioned downstream of the combustor gasoutlet and upstream of heat recovery apparatus (discussed furtherhereinbelow). For example, when operated with pure oxygen, the diameterof the combustor may be smaller at the bottom than the top thereof. Inembodiments, an expander is incorporated after the cyclones (becausecyclone efficiency increases with higher pressures). In embodiments, oneor more expander is positioned upstream of one or more baghouse filters,which may be desirably operated at lower pressures. In embodiments, thesystem comprises an expander downstream of one or more combustorcyclones. The expander may be operable at a pressure greater than 15, 20or 30 psig. The one or more expanders may be operable to recover PVenergy.

Combustion Separator(s)/Heat Recovery:

The superficial velocity selected for the gas/solid separators (whichmay be cyclones) will be selected to maximize efficiency and/or reduceerosion thereof. The cyclones may be operable at a superficial velocityin the range of from about 65 to about 85 feet/s, from about 70 to about85 feet/s, or at about 65, 70, 75, 80, or 85 ft/s.

As shown in FIG. 1, the combustor outlet may be fluidly connected, viacombustor outlet line 106, with one or more combustor particulateseparators 60 (e.g. HTM cyclones). Flue gas is extracted from combustorseparator(s) 60 via particulate-reduced flue gas line 112, whileseparated solids (e.g. HTM) are introduced into GSP 80, for example viadipleg 61. The one or more cyclones may be configured in anyarrangement, with any number of cyclones in series and/or in parallel.For example, a first bank of cyclones (e.g., from 1 to four or morecyclones) operated in parallel may be in series with a second bank ofcyclones comprising from 1 to 4 or more cyclones in parallel and so on.The system can comprise any number of banks of cyclones.

The one or more combustion HTM cyclones may be connected with one ormore ash cyclones, and the ash cyclones may be followed by heatrecovery. In such embodiments, the cyclones are high temperature,refractory-lined or exotic material cyclones. In embodiments, the DFBgasification system comprises two, three or four combustor separators inseries. In embodiments, one to two banks of combustion HTM cyclones arefollowed by one or more banks of ash cyclones. In embodiments, twocombustion HTM cyclones are followed by one or more than one combustorash cyclone. The one or more HTM cyclone may have a performancespecification of greater than 99, greater than 99.9 or greater than99.98% removal of heat transfer material (two or more combustor cyclonesmay be utilized to achieve the desired efficiency). In embodiments, theone or more ash cyclone may be operated to remove ash, for example, inorder to reduce the size of a downstream baghouse(s). In embodiments,the one or more ash cyclones are operable to provide greater than about60%, 70%, 80%, 85% or 90% ash removal from a gas introduced thereto.

In alternative embodiments, heat recovery apparatus is positionedbetween the HTM cyclone(s) and the ash removal cyclone(s). In suchembodiments, combustor flue gas is introduced into one or more combustorHTM cyclones. The gas exiting the one or more HTM cyclones is introducedinto one or more heat recovery apparatus. The gas exiting the one ormore heat recovery apparatus is then introduced into one or more ashcyclones for removal of ash therefrom. The heat recovery apparatus maycomprise one or more selected from the group consisting of airpreheaters (e.g., a combustion air preheater), steam superheaters, wasteheat recovery units (e.g., boilers), and economizers. In embodiments,heat recovery generates steam. In such embodiments comprising heatrecovery upstream of ash removal, the one or more ash removal cyclonesmay not be refractory-lined, i.e. the one or more ash removal cyclonesmay be hard faced, but lower temperature cyclone(s) relative to systemscomprising ash removal upstream of heat recovery. In embodiments, theash removal cyclones are operable at temperatures of less than 400° F.,less than 350° F., or less than 300° F. In embodiments, the lowertemperature ash removal cyclones are fabricated of silicon carbide.

In embodiments, heat recovery is utilized to produce superheated steam.In embodiments, the superheated steam is produced at a temperature inthe range of from about 250° F. to about 400° F. and a pressure in therange of from about 100 psig to about 300 psig.

In embodiments comprising heat recovery upstream of ash recovery, theface of the tubes may be built up and/or the velocity reduced indownward flow in order to minimize erosion of heat recovery apparatus(e.g., heat transfer tubes). The velocity to the cyclones in suchembodiments may be less than 80, 75, 70, or 65 ft/s. If the velocity isreduced appropriately, the ash will not stick to the heat recoveryapparatus (e.g., to waste heat boiler tubes and/or the superheatertubes), and will not unacceptably erode same.

In embodiments, combustor flue gas is introduced directly or indirectlyto the economizer of a boiler for recovery of heat and, for example,power production.

In embodiments, the DFB system comprises one or more disengaging box.Such a disengaging box may be utilized in place of or in addition to thecombustor cyclone(s) and/or the gasifier cyclones(s). Such a disengagingbox may comprise a plurality of channels. Such a disengaging box may bemore desirable on the process gas (gasifier/pyrolyzer) side to furtherensure that HTM is effectively removed from the gasification processgas.

Gasifier Seal Pot (GSP) and Combustor Seal Pot (CSP).

Referring now to FIG. 1, the angle α between the seal pot and the vessel(i.e. between the combustor seal pot and the combustor and/or betweenthe gasifier seal pot and the gasifier) may be in the range of fromabout 5 to about 90°, from about 5 to about 80°, or from about 5 toabout 60°. In embodiments, α is less than 45°. Utilization of a higher agenerally mandates a taller seal pot. Lower angles may be operable withthe use of fluidization/aeration to maintain fluidization. Generally,for α angles between 5 and about 45 degrees, fluidization/aeration mayalso be utilized. In embodiments, a lower angle, such as an angle ofabout 5 degrees, is utilized in the design so that the seal pot (CSPand/or GSP) is relatively short and the overall height of the unit (i.e.the stackup) may be reduced.

As mentioned hereinabove, the seal pot fluidization gas can be orcomprise another gas in addition to or in place of steam. For example,combustor flue gas and/or recycled synthesis gas may be utilized asfluidization gas for the GSP. In embodiments, the fluidization gas forthe CSP, the GSP or both comprises steam. When recycled synthesis gas isutilized for fluidization of the GSP, the synthesis gas is returned tothe gasifier and may provide additional clean synthesis gas from the DFBsystem. By using non-steam as the fluidization gas in the seal pot(s),steam may be reduced or substantially eliminated from the product gas,thus increasing the Wobbe Number thereof, which may be beneficial fordownstream processes (such as, for example, downstream power production,discussed further hereinbelow). In embodiments, upgrader tailgascomprising sulfur is utilized as fluidization gas for the GSP.

Removal of Sulfur Compounds from Product Gasification Synthesis Gas viaUtilization of Wood Ash.

Sulfur may exit the disclosed DFB gasification system with the processgas, the combustor flue gas, and/or with the ash. Removal of the sulfuras a solid may be desired. In embodiments, ash (e.g., wood ash) from theash removal cyclones is utilized to remove mercaptan sulfur and/or H₂Sfrom synthesis gas. In embodiments, mercaptan sulfur and/or H₂S removalis performed at a pH of greater than or about 7.5, 7.7, or 8. Inembodiments, the ash (e.g., wood ash) comprises, for example, NaOHand/or Ca(OH)₂. In embodiments, a sulfur extraction material is addedwith the heat transfer material, such that sulfur may be removed withash. The sulfur extraction material may comprise a calcium material,such as calcium oxide (CaO), which may be converted to calcium sulfideand exit the system as a solid. In embodiments, ash water (comprisingNaOH and/or Ca(OH)₂) is utilized to scrub sulfur from the outlet gases.For example, the system may comprise a scrubbing tower for cleaning theprocess gas. Depending on the basicity of the ash water, it may beutilized, in embodiments, as scrubbing water. Such scrubbing may beperformed upstream of an ESP or other particulate separator configuredto remove particulates.

Except for air, the different fluidization gases mentioned for the CSPmay be utilized for the GSP as well. (In embodiments, a percentage ofair (e.g., less than 4 volume percent) may be utilized on the GSP toprovide higher temperature in the gasifier). The fluidization gas on theGSP may be selected from the group consisting of flue gas, steam,recycled synthesis gas, and combinations thereof.

In embodiments, the seal pots are round. In embodiments, the seal potsare rectangular. In embodiments, the seal pots are square. Inembodiments, the operating pressure is less than about 15 psig and theseal pots are not round. The use of square and/or rectangular seal potdesigns may allow for closer spacing therebetween.

For the GSP, the minimum fluidization velocity for the heat transfermaterial is set at any point in time. That is, the minimum initialfluidization velocity is determined by the initial average particle size(e.g., 100 μm). After a time on stream (for example, 120 days), the heattransfer material may have a reduced average particle size (e.g., about25 μm); thus the minimum fluidization velocity changes (decreasing withtime on stream/HTM size reduction). The CSP and GSP may be selected suchthat they have a size suitable to handle the highest anticipatedfluidization velocity, i.e. generally the start-up value. Inembodiments, the minimum fluidization velocity of the GSP is initiallyhigh and decreases with time. However, it is possible that, ifagglomerization occurs, the minimum fluidization velocity may increase.The minimum fluidization velocity is determined by the heat transfermaterial, in particular by the average particle size, the density,and/or the void fraction thereof. In embodiments, the minimumfluidization velocity is greater than about 0.2 ft/s. In embodiments,the minimum fluidization velocity is greater than about 1.5 ft/s. As theparticle size distribution (PSD) decreases, seal pot fluidizationvelocity decreases.

The diameter of the seal pots may be set by the number of diplegpenetrations, i.e. how many cyclones you have and/or by the angles atwhich the diplegs enter into the seal pot. Diplegs may be angled toallow shorter dipleg length. In embodiments, combustor cyclone diplegsenter the top of the gasifier seal pots, as with the CSP (where gasifiercyclone diplegs enter the CSP). The CSP and/or the GSP may contain adistributor configured for distributing gas uniformly across thecross-section (e.g., the diameter) thereof. In embodiments, thedistributor is positioned at or near the bottom of the CSP and/or theGSP. In embodiments, to minimize/avoid erosion of the seal leg, theminimum distance between the distributor (i.e. the fluidization nozzles)at the bottom of the seal pot (GSP and/or CSP) and the bottom of thedipleg(s) projecting thereinto is 10, 11, 12, 13, 14, 15, 16, 17 or 18inches. In embodiments, there is a distance of more than 15, 16, 17 or18 inches between the seal pot distributor and the cyclone dipleg(s).Desirably, the dipleg-to-dipleg spacing and/or the dipleg-to-refractoryID spacing is at least 10, 11 or 12 inches. In embodiments, thedipleg-to-dipleg spacing and the dipleg-to-refractory ID spacing is atleast about 12 inches. In embodiments, the diplegs are supported. Suchsupport may be provided to minimize/prevent vibration of the diplegs.For the GSP, the seal may actually be within the dipleg of the combustorcyclone(s) and the GSP (since gasifier 20 is at a higher pressure thancombustor separator 60).

The GSP is designed with an adequate head of heat transfer material tominimize backflow. The height of the GSP is based on a design margin. Inembodiments, the design margin is in the range of from about 1 psig toabout 5 psig, or is greater than or about equal to 1, 2, 3, 4, or 5psig. The head of heat transfer material (e.g., sand) will provide theΔP (pressure drop) at least sufficient to prevent backflow ofgas/prevent gasifier backflowing into the combustor cyclone. Thedistribution of nozzles in both the CSP and the GSP may be in the rangeof from about one to about four nozzles per square foot. In embodiments,the distributors in any or all vessels (gasifier, combustor, CSP andGSP) comprise from about one to about four nozzles per ft².

In embodiments, one or more of the seal pots (either or both a combustorseal pot, CSP, and/or a gasifier seal pot, GSP) is replaced with an Lvalve or a J valve. In embodiments, the disclosed DFB gasificationsystem comprises one or more J valves in place of a CSP. In embodiments,the DFB gasification system comprises one or more J valves in place of aGSP. In embodiments, the DFB gasification system comprises multipleCSPs. In embodiments, the multiple CSPs are substantially identical. Inembodiments, the DFB gasification system comprises multiple GSPs. Inembodiments, the multiple GSPs are substantially identical. Inembodiments, the disclosed gasification system comprises at least one orone CSP and at least one or one GSP. The seal of the CSP may be withinthe CSP (while the seal on the GSP may simply be within a dipleg). Inembodiments, a J valve is utilized on the gasifier rather than a GSP.

The height of the CSP is determined by the pressure needed for the seal,which is the differential pressure between the gasifier cyclone and thecombustor. The combustor pressure plus a design margin may be utilizedto determine the desired height of the CSP (i.e. the desired height ofthe heat transfer material therein). In embodiments, the pressure isnear atmospheric. In embodiments, the ΔP is greater than 2 psig. Inembodiments, the ΔP is in the range of from about 2 psig to about 25psig, from about 2 psig to about 20 psig, or from about 2 psig to about15 psig. In embodiments, the pressure differential is about 10, 12, 15,or 20 psig. Desirably, the ΔP is not less than about 2 psig, as pressureequalization is undesirable. In embodiments, a smaller ΔP is utilized,thus allowing the use of a shorter CSP 70.

Downstream Systems.

The DFB gasification system may further comprise apparatus 100downstream of the dual fluidized bed gasifier. For example, downstreamapparatus 100 may include one or more selected from Fischer-Tropschsynthesis apparatus, power production apparatus, non-Fischer-Tropschchemical production apparatus, tar removal apparatus, heat recoveryapparatus, carbon dioxide removal apparatus, scrubbers, expanders, andcombinations thereof. In FIG. 1, line 117 indicates generically theremoval of product and/or byproduct (e.g. tar, tar-reduced gas, FTsynthesis products, FT tailgas, PU tailgas, scrubbed gas, power,upgraded product, chemicals, fuels, carbon dioxide, carbon-dioxidereduced gas, etc.) from downstream apparatus 100.

In embodiments, the DFB gasification system is integrated into a biomassto fuels and/or biomass to power system. In embodiments, both power andFischer-Tropsch fuels are produced from the gaseous products of thedisclosed DFB gasifier. In embodiments, the DFB gasification system isintegrated with power production apparatus, whereby the system isutilized for (e.g., primarily for) the production of power. Inembodiments, the system is integrated with Fischer-Tropsch synthesisapparatus and used utilized primarily for the production of liquid fuels(e.g., Fischer-Tropsch fuels).

In embodiments, from about 10 to about 30% of the product synthesis gasfrom a DFB as disclosed herein is bypassed to power generation and atleast a portion of the remaining product gas is utilized for theproduction of Fischer-Tropsch fuels. In such embodiments, at least aportion of the Fischer-Tropsch tailgas from the production ofFischer-Tropsch fuels may be blended with the bypass synthesis gas toprovide a gas with a suitable Wobbe number for the production of power.FIG. 2 is a schematic of an integrated system 10A comprising a dualfluidized bed gasification system'/gasifier' 110 according to thisdisclosure, and downstream apparatus 100A configured for Fischer-Tropschsynthesis and power production. Gasification system 110 is as describedwith regard to gasification system 10 in FIG. 1. Integrated system 10Acomprises DFB gasifier 110, power production apparatus 140, andFischer-Tropsch synthesis apparatus 130. Carbonaceous feed is gasifiedin the DFB gasifier 110, as described hereinabove, producing ‘dirty’synthesis gas. Integrated system 10A may comprise apparatus 120configured for cleaning up the ‘dirty’ synthesis gas to provide asynthesis gas having fewer undesirable components (i.e. having reducedamounts of hydrogen, carbon monoxide, carbon dioxide, water vapor,hydrogen sulfide, and/or etc.) and/or a desired molar ratio of hydrogento carbon monoxide. For example, apparatus 120 may comprise a partialoxidation apparatus fluidly connected via line 115 with the DFB gasifier110, and configured to subject the ‘dirty’ synthesis gas to oxidation,producing a ‘clean’ synthesis gas. A POx reactor may be operable at atemperature of greater than or about 2000° F., 2100° F., or 2200° F.Oxygen may be introduced into the apparatus 120 (e.g. a POx reactor) vialine 116. A line 125 may be configured to introduce at least portion ofthe ‘cleaned’ synthesis gas from clean-up apparatus 120 into, forexample, a Fischer-Tropsch production reactor of FT synthesis apparatus130. A line 126 may be configured to introduce at least a portion of thesynthesis gas into power production apparatus 140, configured for theproduction of power.

The Fischer-Tropsch synthesis reactor 130 may be any suitableFischer-Tropsch reactor known in the art. In embodiments, theFischer-Tropsch synthesis reactor comprises an iron-based catalyst. Inembodiments, the Fischer-Tropsch synthesis reactor comprises acobalt-based catalyst. In embodiments, the catalyst is a precipitatediron catalyst. In embodiments, the precipitated Fischer-Tropsch catalystis an iron-based catalyst formed as described in or having thecomposition of Fischer-Tropsch catalyst described in U.S. Pat. No.5,508,118 and/or U.S. patent application Ser. Nos. 12/189,424;12/198,459; 12/207,859; 12/474,552; and/or 12/790,101, the disclosure ofeach of which is hereby incorporated herein in its entirety for allpurposes not contrary to this disclosure.

Fischer-Tropsch production reactor 130 produces Fischer-Tropsch tailgasand a variety of products that are generally liquids at the operatingtemperature of the Fischer-Tropsch reactor. The liquid Fischer-Tropschproducts may comprise primarily hydrocarbons. The liquid Fischer-Tropschproducts may comprise primarily long-chain aliphatic hydrocarbons.Tailgas may be removed from Fischer-Tropsch reactor 130 via a tailgasline 136 and Fischer-Tropsch synthesis products may be removed via line137 and/or 135.

Integrated system 10A may further comprise product upgrading apparatus130B configured to upgrade the liquid products of the Fischer-Tropschsynthesis and fluidly connected with Fischer-Tropsch synthesis apparatus130 via line 135, whereby at least a portion of the liquid products ofthe Fischer-Tropsch reactor 130 may be upgraded to more desiredproducts. The product upgrading apparatus 130B may comprisehydrotreating apparatus, hydrocracking apparatus, hydroisomerizationapparatus, and/or any other product upgrading apparatus known to thoseof skill in the art. The products of Fischer-Tropsch reactor 130 and/orthe product upgrading apparatus 130B removed via lines 137 and 138,respectively, may comprise primarily jet fuel, primarily diesel fuel,primarily gasoline, primarily naphtha, or some combination of one ormore selected from jet fuel, diesel fuel, gasoline, and naphtha.

Upgrading may create an upgrader tailgas, removed from integrated system10A via line 139. As discussed hereinabove, such upgrader tailgas may beutilized as fuel for the combustor of the DFB gasification system 110,and/or as fluidization gas in a CSP, a GSP, and/or the gasifier thereof.In such embodiments, upgrader tailgas outlet line 139 may fluidlyconnect product upgrader 130B with combustor 30, with CSP 70, with GSP80, and/or with gasifier 20.

Power production apparatus 140 may be any apparatus known in the art forthe production of power, indicated in FIG. 2 via line 145. Inembodiments, power production apparatus 140 comprises a gas turbine. Inembodiments, at least a portion of the tailgas removed fromFischer-Tropsch synthesis reactor 130 via line 136 is introduced intopower production apparatus 140. In embodiments, a portion of theFischer-Tropsch tailgas is utilized for power production and a portionis utilized in the DFB gasifier of gasification system 110, as discussedin detail hereinabove. For example, a portion of the Fischer-Tropschtailgas may be utilized as fuel for the combustor of the DFBgasification system 10/110, and/or as fluidization gas in a CSP, a GSP,and/or the gasifier thereof. In such embodiments, FT tailgas outlet line136 may be fluidly connected with combustor 30, with CSP 70, with GSP80, and/or with gasifier 20.

In embodiments, a DFB gasification system of this disclosure furthercomprises a tar removal system downstream from the gasifier cyclones andconfigured for removal of tar from the product synthesis gas. Inembodiments, the tar removal system is downstream heat recoveryapparatus. The tar removal system may comprise a Dahlman unit, whichcomprises a multistage solvent (i.e. oil) wash. The Dahlman unit may beoperable with synthesis gas at a temperature of at least or about 650°F., 700° F., 750° F., 800° F., 850° F., or 900° F. As discussedhereinabove, a portion of the removed tars may be recycled to thecombustor of the DFB gasification system for use as fuel.

In embodiments, the DFB gasification system further comprises a POxunit, a boiler or a NiDFB (mentioned hereinabove) downstream of thegasifier. In embodiments, the synthesis gas is provided for downstreamproduction of chemicals and the DFB gasification system furthercomprises downstream apparatus for the production of chemicals and/orfuels other than Fischer-Tropsch fuels and/or chemicals. The downstreamapparatus may be any apparatus known in the art configured for theproduction of methanol, ethanol, ammonia, fertilizer, etc., fromgasification gas comprising hydrogen and carbon monoxide.

In embodiments, a system for the production of jet fuel is provided, thesystem comprising a DFB gasifier as disclosed herein, tar reformingapparatus, one or more slurry Fischer-Tropsch reactors, hydrocrackingapparatus and/or hydrotreating apparatus.

Features/Advantages:

The disclosed system and method enable the production of gas by use of ahigh throughput pyrolyzer and an external combustor, incorporatingcirculation of a heat transfer material to provide heat for theendothermic gasification reactions. Via the disclosed system and method,exothermic combustion reactions are separated from endothermicgasification reactions. The exothermic combustion reactions take placein or near a combustor while the endothermic gasification reactions takeplace in the gasifier/pyrolyzer. This separation of endothermic andexothermic processes may provide a high energy density product gaswithout the nitrogen dilution present in conventional air-blowngasification systems.

While preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Where numerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, and so forth). Use ofthe term “optionally” with respect to any element of a claim is intendedto mean that the subject element is required, or alternatively, is notrequired. Both alternatives are intended to be within the scope of theclaim. Use of broader terms such as comprises, includes, having, etc.should be understood to provide support for narrower terms such asconsisting of, consisting essentially of, comprised substantially of,and the like.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the preferred embodiments of the present invention.The disclosures of all patents, patent applications, and publicationscited herein are hereby incorporated by reference, to the extent theyprovide exemplary, procedural or other details supplementary to thoseset forth herein.

1. A system configured for the production of at least one productselected from the group consisting of synthesis gas, Fischer-Tropschsynthesis products, power, and chemicals, the system comprising: a dualfluidized bed gasification apparatus comprising: a gasifier and acombustor, wherein the combustor is configured for heating a particulateheat transfer material, thus producing a combustor flue gas; andwhereinthe gasifier is configured to receive the heated particulate heattransfer material and a carbonaceous feedstock, whereby the heatedparticulate heat transfer material provides heat for endothermicgasification of the carbonaceous feedstock, thus producing agasification product gas comprising hydrogen and carbon monoxide, andentrained particulate material; and at least one particulate separatorselected from the group consisting of gasifier particulate separatorsconfigured to separate gasification product gas from the entrainedproduct; and combustor particulate separators configured to separateheated particulate heat transfer material from the combustor flue gas;and at least one apparatus selected from the group consisting of powerproduction apparatus configured to produce power from at least a portionof the gasification product gas, partial oxidation reactors configuredfor oxidation of at least a portion of the gasification product gas, tarremoval apparatus configured to reduce the amount of tar in thegasification product gas, Fischer-Tropsch synthesis apparatus configuredto produce Fischer-Tropsch synthesis products from at least a portion ofthe gasification product gas, chemical production apparatus configuredfor the production of at least one non-Fischer-Tropsch product from atleast a portion of the gasification product gas, and dual fluidized bedgasification units configured to alter the composition of at least aportion of the gasification product gas.
 2. The system of claim 1further comprising at least one expander downstream of at least onecombustor particulate separator.
 3. The system of claim 2 furthercomprising heat recovery apparatus downstream of the at least oneexpander.
 4. The system of claim 1 comprising at least one combustorparticulate separator that is a cyclone, wherein the at least onecombustor cyclone is operable at a superficial velocity in the range offrom about 70 to about 85 ft/s.
 5. The system of claim 1 comprising (a)at least one primary gasifier particulate separator configured toseparate particulate heat transfer material from the entrained product,thus providing a particulate-reduced product comprising ash, and atleast one secondary gasifier particulate separator configured toseparate particulate heat transfer material from the particulate-reducedproduct, (b) at least one primary combustor particulate separatorconfigured to separate particulate heat transfer material from the fluegas, thus providing a particulate-reduced flue gas comprising ash, andat least one secondary combustor particulate separator configured toseparate particulate heat transfer material from the particulate-reducedflue gas; or both (a) and (b).
 6. The system of claim 5 configured forintroduction of the separated particulate materials from the primarygasifier particulate separator, the secondary gasifier particulateseparator, or both into the combustor for heating therein.
 7. The systemof claim 5 further comprising a scrubber downstream of the secondarygasifier particulate separator, a scrubber downstream of the secondarycombustor particulate separator, or both, wherein the scrubber isconfigured to scrub sulfur from a gas introduced thereto, via contactthereof with a liquid comprising at least a portion of the ash.
 8. Thesystem of claim 5 wherein the at least one primary gasifier particulateseparator, the at least one primary combustor particulate separator, orboth is configured for removal of greater than 99, 99.9, or 99.98 weightpercent of the particulate heat transfer material from a gas introducedthereto.
 9. The system of claim 8 wherein the at least one secondarygasifier particulate separator, the at least one secondary combustorparticulate separator, or both is configured for removal of greater thanabout 60, 70, 80, 85, or 90 weight percent of the ash from a gasintroduced thereto.
 10. The system of claim 1 further comprising one ormore heat recovery apparatus configured for recovery of heat from thegasification product gas, from the combustor flue gas, or from both thegasification product gas and the combustor flue gas.
 11. The system ofclaim 10 wherein the at least one heat recovery apparatus comprises atleast one component selected from the group consisting of airpreheaters, boiler feedwater preheaters, steam superheaters, waste heatboilers, waste heat superheaters, and economizers.
 12. The system ofclaim 11 comprising an air preheater configured to recover heat from thegasification product gas and introduce it into the combustor.
 13. Thesystem of claim 10 comprising (a) at least one heat recovery apparatuslocated downstream of the at least one primary gasifier particulateseparator, (b) at least one heat recovery apparatus located downstreamof the at least one primary combustor particulate separator, or both (a)and (b).
 14. The system of claim 10 comprising (a) at least one heatrecovery apparatus located upstream of the at least one secondarygasifier particulate separator, (b) at least one heat recovery apparatuslocated upstream of the at least one secondary combustor particulateseparator, or both (a) and (b).
 15. The system of claim 14 wherein theat least one secondary particulate separator downstream of the at leastone heat recovery apparatus is operable at a temperature of less thanabout 400° F.
 16. The system of claim 1 further comprising heat recoveryapparatus downstream of at least one particulate separator.
 17. Thesystem of claim 1 further comprising at least one sealing apparatusselected from seal pots and valves configured to prevent backflow ofmaterial from the combustor into the at least one gasifier particulateseparator or from the gasifier into the at least one combustorparticulate separator.
 18. The system of claim 17 comprising a valveselected from J-valves and L-valves.
 19. The system of claim 18comprising a J-valve configured to prevent backflow of material from thegasifier into at least one combustor particulate separator.
 20. Thesystem of claim 17 comprising at least one seal pot selected fromcombustor seal pots configured to prevent backflow of material from thecombustor into the at least one gasifier particulate separator andgasifier seal pots configured to prevent backflow of material from thegasifier into the at least one combustor particulate separator.
 21. Thesystem of claim 20 wherein the at least one seal pot is configured foroperation at a minimum fluidization velocity of greater than about 0.2ft/s.
 22. The system of claim 21 wherein the at least one seal pot isconfigured for operation at a minimum fluidization velocity of greaterthan about 1.5 ft/s.
 23. The system of claim 20 wherein the pressuredrop across the at least one seal pot is at least 2 psig, is less thanabout 20 psig, or both.
 24. The system of claim 20 wherein the at leastone particulate separator comprises a dipleg extending from at or near abottom thereof, and wherein the dipleg extends a distance into the atleast one seal pot from at or near a top thereof
 25. The system of claim24 wherein the at least one seal pot comprises a distributor and whereinthe dipleg of the at least one particulate separator extends to adistance no less than about 10, 11, 12, 13, 14, 15, 16, 17, or 18 inchesfrom the seal pot distributor.
 26. The system of claim 24 wherein theminimum distance from the dipleg to a side or bottom of the seal pot isat least 10 inches.
 27. The system of claim 20 comprising at least twogasifier particulate separators, each comprising a dipleg extending adistance into a combustor seal pot; at least two combustor particulateseparators, each comprising a dipleg extending a distance into agasifier seal pot; or both, wherein the minimum dipleg to diplegseparation within a seal pot is at least 10 inches.
 28. The system ofclaim 20 wherein an angle selected from the group consisting of an angleformed between an at least one combustor seal pot and the combustor andan angle formed between an at least one gasifier seal pot and thegasifier is in the range of from about 5° to about 90°.
 29. The systemof claim 28 wherein the angle is less than about 45°.
 30. The system ofclaim 20 comprising at least one combustor seal pot, wherein the atleast one combustor seal pot is fluidized by a combustor seal potfluidization gas.
 31. The system of claim 30 wherein the combustor isconfigured for fluidization with a combustor fluidization gas comprisingprimarily air or oxygen.
 32. The system of claim 31 configured forintroduction of at least or about 20% of the combustor fluidization gasneeded in the combustor via the at least one combustor seal pot.
 33. Thesystem of claim 20 wherein at least one seal pot is substantially roundor rectangular.
 34. The system of claim 33 wherein at least one seal potis substantially rectangular and wherein the operating pressure of theat least one rectangular seal pot is less than about 15 psig.